Copper topped piston



July 20, 1948. BOYD 2,445,309

COPPER TOPPED PISTON Filed Sept. 22, 1944 Inventor landonfiwfio yalwwrazz.

i 'l' I\ 7 I v 7 Patented July 20, 1948 vUNITED STATES PATENT OFFICE2,445,309 COPPER TOPPED PISTON Landon B. Boyd, La. Porte, Ind.

Application September 22, 1944, Serial No. 555,293

9 Claims.

This invention relates to a copper topped piston and has for one objectto provide a ferrous piston having a thin copper top or deck on itsupper surface.

Another object is to provide a method of permanently securing the copperdeck to the outer surface of the piston head.

Another object is to define a ielationship between the thickness of thecopper deck and its diameter.

Other objects will appear from time to time throughout the specificationand claims.

The invention is illustrated more or less diagrammatically in theaccompanying drawings, wherein:

Figure 1 is a vertical section through one form of the piston;

Figure 2 is a plan view of one form of the piston before the copper deckhas been secured in place;

Figure 3 is a side elevation in part section, showing a modified form ofpiston.

Like parts are indicated by like characters throughout the specificationand the drawings.

The invention is not limited to any particular type of piston or pistonconstruction, and those illustrated are merely typical examples of pos--sible piston constructions.

In general, the invention is embodied in a ferrous piston, to the top ordeck of which is applied a thin coating of copper. This copper coatingcan be applied by various methods.

In the example shown in Figure 1, the invention is embodied on a ferrouspiston having a main part I with ring grooves 2 and the other necessaryconstruction for a piston. Permanently secured on the top of the pistonis a copper deck 3. I

The upper surface of the ferrous piston may be smooth or roughened. Onesuitable form of roughening is that shown in Figure 2, in which thepiston head portion 4 is provided with a series of concentric grooves orserrations 5, which may be made in any manner by machining or casting orotherwise. Any such roughenings or irregularities provide a more secureanchorage for the copper on the ferrous top.

In the modified form of Figure 3, the main piston body 6 is providedwith ring grooves I and a peripheral upstanding flange 8. A copper deck8 is positioned on the head of the piston and within the space boundedby the upstanding peripheral flange 8.

In forming the piston, the copper is preferably as pure as possible andis free from oxides and all forms of impurities. The copper may be inalmost any form when it is secured on the head of the ferrous piston. Itmight be in the form of a disc. Experience has shown, however, that oneof the convenient ways of applying the copper is to put upon the uppersurface of the piston a measured quantity of relatively finely dividedcopper, such as copper shot." If this is done, a dam or peripheralupstanding flange of metal surrounds the copper. This dam or peripheralupstanding flange of metal can be cast or machined on the ferrouspiston, and when the copper is in molten form, it will not spill over atthe time it is processed in a high temperature furnace. The copper, inwhatever form it is used, is placed upon the piston head, and togetherthey are subjected to a heating in a furnace at a sufflcient temperatureto cause the copper and the ferrous piston body to become permanentlybonded or brazed together.

While the invention is not limited to the use of a flux or in fact toany particular flux, it is convenient for general purposes to use aflux, and one suitable flux includes the following inredients:

Per cent Manganese dioxide 25 Borax '15 and to this amount add Finecopper powder (by weight) 25 The materials above listed are then mixedpreferably with any non-petroleum oil as a vehicle to a consistency ofthin paint, and they are applied to the surface of the ferrous pistonhead to which the upper disc is to be brazed or fixed.

One of the reasons for providing a copper deck on a piston is to reducepiston heating. Experience has shown that if t e copper deck is toothick it does not produce this result. Furthermore, if a too thick deckof copper is used it will hold sufliicient heat so that it will conductthis heat rapidly to the body of the piston. If the copper deck is toothin, it cannot absorb the heat of combustion in sufficient quantities,and, on the succeeding cycles, it may not have retained suflicient heatto emit it in the quantities necessary for the correct operation of thepiston.

The thickness of the copper deck must bear a specific relationship tothe diameter of the piston itself. The effect of a copper deck of theproper thickness is apparently to act as a heat discharging member, sothat heat which enters the copper disc does not in the main penetrate toand is not in the main conducted to the body 8 of the piston, but isdischarged again into the combustion space. In this sense, the coppermay be considered as a heat-reflective agent, or if the heat enters thebody of the copper deck, it is reflected outward again from the innersurface of the copper deck or from some point which is between the innerand the outer surface of the deck, and this is given up again into thecombustion space and is prevented from entering the body of the piston.Practical tests have shown that pistons equipped with copper decksproportioned according to the formula and explanation given below resultin keeping the piston substantially cooler than is the case where thepiston is formed of other materials, and particularly where the pistonis formed entirely of a ferrous metal or alloy.

There is set out below an algebraic formula by means of which thethickness of a copper deck for a given diameter of piston may be readilydetermined. In the explanation the expresison "mean thickness appears.In some cases the upper surface of the head of the ferrous piston issmooth. In that case the thickness of the deck may be uniform. In cases,however, where the upper surface of the ferrous piston is roughened,serrated or grooved, the expression "mean thickness means the thicknesshalf way between the serrations, grooves or irregularities and the deck.The formula and its explanation are as follows:

X=mean thickness of copper deck Y=a constant used in the equation andshown in table set out below D=diameter of piston B=coefllcient multiple(The expression coeificient multiple" means the number of times thecoefficient of iron will divide into the coefficient of copper. For thesake of simplicity this is taken at a ratio of 4 to 1 rather thancarrying it out to the fifth and sixth decimal places in a completecalculation.)

Inches in Diameter Constant For pistons of approximately 8 inches ofdiameter and up, a copper deck thickness of approximately a, inch issatisfactory. The thickness of the copper deck for a piston of adiameter between any two diameters above given is calculated byinterpolation between the constants for the said diameters. Thus for apiston 01 3% inches diameter, the constant Ywill be between 4360 and5270.

The formula above is accurate as indicated for general commercialdiameters of pistons. In practical and laboratory tests, it has beenproved accurate as applied to pure copper. Obviously if othernon-ferrous metals were used instead of copper, because of theirdifferent coefficients of heat conductivity, a different constant wouldbe used.

The details of the brazing cycle form no part of the present inventionand are not disclosed in detail herewith. Any heating cycle which willcause the copper to be permanently bonded to the ferrous piston issuitable. Many methods of brazing copper on ferrous metals are now knownand in practice. Hydrogen brazing that is to say, brazing in a furnacewith any reducing atmosphere-may be used for the brazing heating. Ingeneral, all that is required of the heating cycle of this invention isthat the copper be adequately bonded to the ferrous metal of the pistonand that the physical properties of the ferrous metal be not renderedunsatisfactory.

I have set out above a method of producing and a method of calculating apiston which includes a ferrous main structure and a copper deck. Suchpistons have been highly successful both from a point of view of a longengine life, long piston life and improved engine eificiency. Pistonsmade as described above have operated for long periods of time inpractical commercial use with outstanding success. Pistons for enginesof various sizes and types can be made if the instructions above givenare followed. The theoretical explanation of the successful operation ofsuch pistons set out above is believed to be valid and accurate.However, the successful results are proved and can be repeated byfollowing the teachings above set out, irrespective of any theoreticalconsiderations of operation.

I claim:

1. A copper topped piston comprising a main ferrous piston body and athin desk of pure copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to thefollowing formula:

X equalling the mean thickness of the copper deck, D the diameter of thepiston, B the heat transmission coefllcient multiple of the copper, andY a factor varying with the piston diameter.

2. A copper topped piston comprising a main ferrous piston body and athin deck of copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to thefollowing formula:

X equalling the mean thickness of the copper deck, D the diameter of thepiston, B the heat transmission coefllcient multiple of the copper, andY a factor whose value is determined by the piston diameter.

3. A copper topped piston comprising a main ferrous piston body and athin deck of copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to th followingformula:

X equalling the mean thickness of the copper deck, D th diameter of thepiston, B the heat transmission coefficient multiple of the copper, andY equalling a factor of the order of 4360 for a piston having a diameterbetween 2 inches and 3% inches, and a factor of the order of 5270 for apiston having a diameter between 3 inches and 3% inches, and a factor ofthe order of 6400 for a piston having a diameter between 4 inches and 4inches, and a factor of the order of 8540 for a piston having a diameterbetween 4% inches and 5% inches, and a factor of the order of 10,800 fora piston having a diameter between 5 inches and 6 inches, and a factorof the order of 13,000 for a piston having a diameter between 6 inchesand 7 inches.

4. Av copper topped piston comprising a main ferrous piston body and athin deck of copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to thefollowing formula:

X X equalling the means thickness of the copper deck, D the diameter ofthe piston, B the heat transmission coefficient multiple of the copper,

and Y equalling a factor of the order of 4360 for a piston having adiameter between 2 inches and 3% inches.

5. A copper topped piston comprising a main ferrous piston body and a.thin deck of copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to thefollowing formula:

X equalling the mean thickness of the copper deck, D the diameter of thepiston, B the heat transmission coefficient multiple of the copper, andY equalling a factor of the order of 5270 for a piston having a diameterbetween 3% inches and 3% inches.

6. A copper topped piston comprising a main ferrous piston body and athin deck of copper bonded to the upper surface of said piston, thethickness of said copper deck being calculated according to thefollowing formula:

X equalling the mean thickness of the copper deck, D the diameter of thepiston, B the heat transmission coemcient multiple of the copper, and Yequalling a factor of the order of 6400 for a piston having a diameterbetween 1' inches and 4% inches.

'7. A copper topped piston comprising a main ferrous piston body and athin deck of copper bonded to the upper surface of said piston, the

thickness of said copper deck being calculated according to thefollowingformula:

Bur "T X equalling the mean thickness of the copper deck, D the diameterof the piston, B the heat transmission coefficient multiple of thecopper, and Y equalling a factor of the order of 10,800

'for a piston having a diameter between 5% inches and 6 inches.

9. A copper topped piston comprising a main ferrous piston body and athin deckof copper bonded to the upper surface of said piston, thethickness of said copper deck being calculatedaccording to the followingformula:

X equalling the mean thickness of the copper deck, D the diameter of thepiston, B the heat transmission coefficient multiple of the copper, andY equalling a factor of the order of 13,000" for a piston having adiameter between 6% inches. and 7% inches.

LANDON B. BOYD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

